How to Beat the Fume Knight
The Fume Knight is the final boss of the Crown of the Old Iron King. He is found at the very bottom of the Brume Tower.
Weaknesses
Fume Knight is quite the durable fighter, but he seems to take slightly more damage from Magic based attacks. Fire and Lightning seemed to deal no bonus damage. Other elements are unconfirmed.
Melee Characters
Melee characters, whether heavy or light builds, will need to rely on well times dodges to win this fight. During the first half of the fight, Fume Knight will use a large sword and his massive great sword. During this phase, you can block attacks, however it will eat up huge chunks of your stamina. Instead you should just back away, or dodge forward and around the attacks.
Your best time to hit will be when he swings the ultra greatsword, however you can probably sneak in a single hit here and there as he finishes his quicker combos. Once the boss reaches 50-60% health, he will ditch his one sword, and buff his ultra greatsword with dark fire.
The next phase of the fight, can be easier if your dodge timing is on point. He will gain two special attacks. A forward sweep that has him dealing much greater magical damage, and an AoE where he plunges his sword in the ground, causing an explosion. The second also releases magic orbs that must be dodged as well. The rest of his attacks will be straight forward combos, with a few quick swipes, or sometimes utilizing a lunge attack.
During the last phase, you simply must dodge his attacks. Do so by rolling towards his left side. This is the side where he holds his sword, which makes it safer in general to be near, as most of his attacks will end with his sword on his right. Blocking isn't an option anymore, unless you are using a gigantic shield, as each hit will take nearly all your stamina. Be PATIENT, this is just an endurance fight from here on in. Only strike once, twice at the max, and dodge constantly, and you will eventually win the fight.
Ranged Characters
This battle is going to be tough for anyone who prefers ranged combat. For this reason, it is highly suggested you summon the NPC Steelheart Ellie. She can be found at the nearby bonfire. She can act as a tank while you sling spells or arrows at the boss, making it much easier.
Other than that, dress lightly for dodges, and even if you don't usually, bring a shield, in the event you get stuck in a bad spot and simply need to block instead of dodge. Be prepared to cast a lot of spells, so it might be wise to equip the herbs needed to recover your spell uses, as magic has been rebalanced a lot lately, so you will be slinging many more spells than usual during this tough fight.